Metal effect pigments for use in the cathodic electrodeposition painting, method for the production and use of the same, and electrodeposition paint

ABSTRACT

The invention relates to electrocoat material pigments, said electrocoat material pigments comprising metal effect pigment platelets coated with at least one coating material, said coating material comprising one or more functional groups for adhesion or attachment to the pigment surface and at least one amino-functional group, said amino-functional group being protonatable or positively charged. The invention further relates to a process for producing these electrocoat material pigments and to the use thereof, and to a cathodic electrocoat material which comprises the inventive pigments.

The invention relates to pigments based on metal effect pigmentplatelets which can be deposited in the course of cathodicelectrocoating. The invention further relates to a process for producingthese electrocoat material pigments and to the use thereof in a cathodicelectrocoat material or in cathodic electrocoating. The inventionfinally also relates to a cathodic electrocoat material.

Electrocoating (EC) is a process for applying particular water-solublecoating materials, so-called electrocoat materials, to electricallyconductive substrates, for example a workpiece. Between a workpieceimmersed into a coating bath and a counterelectrode, an electricaldirect current field is applied. A distinction is drawn between anodicdeposition, so-called anodic electrocoating (AEC), in which theworkpiece is connected as the anode or plus pole, and cathodicdeposition, so-called cathodic electrocoating (CEC), in which theworkpiece is connected as the cathode or as the minus pole.

The coating material binder contains functional groups of particularpolarity, which are present in salt form due to neutralization and as aresult colloidally dissolved in water. In the vicinity of the electrode(within the diffusion boundary layer), owing to hydrolysis, hydroxideions form in CEC or H⁺ ions in AEC. These ions react with the bindersalt, causing the functionalized binders to lose their salt form(“salting out”), become insoluble and coagulate at the surface of theworkpiece. Later, the coagulated binder particles lose water owing toelectroosmosis procedures, which causes further compaction. Finally, theworkpiece is withdrawn from the immersion bath, freed of noncoagulatedcoating material particles in a multistage rinsing process and fired attemperatures of 150-190° C. (Brock, Groteklaes, Mischke, “Lehrbuch derLacktechnologie” [Textbook of coating technology] 2^(nd) edition,Vincentz Verlag 1998, p. 288 ff.).

Electrocoating has several economic and ecological advantages overconventional coating methods such as wet coating or powder coating.

A primary factor which should be mentioned here is the comparativelyexactly adjustable layer thickness. Compared to powder coatings,electrocoating also homogeneously coats difficult-to-access parts of theworkpiece. This results from the following fact: first, the depositionof the binder takes place at points of high field strength, such ascorners and edges. However, the film which forms has a high electricalresistance. The field lines therefore shift to other regions of theworkpiece and are concentrated toward the end of the coating operationentirely on the most inaccessible points, for example regions or pointsin the interior of the workpiece (inner coating). The coating ofparticularly difficult-to-access points of a workpiece can be improvedonce more by the provision of auxiliary electrodes. With electrocoating(EC) it is therefore possible to coat workpieces of any shape, providedthat they are electrically conductive. EC is additionally associatedadvantageously with properties such as minimal solvent emissions,optimal material yield and noncombustibility. Droplet- and run-freepaintwork is obtained. Electrocoating is performed in an automatedmanner and is as a result a very inexpensive coating method, especiallysince it can be performed at comparatively low current densities of afew mA/cm².

Owing to the simple and highly inexpensive application method,electrocoating at present finds use in numerous systems. The most commonare basecoats, for example in automotive OEM finishing, and single-layertopcoats. Electrocoats are found, for example, on radiators, controlcabinets, office furniture, in construction, in iron and householdproducts, in storage technology or in rack construction, in climatecontrol and lighting technology, and in apparatus construction andmechanical engineering.

Compared to the older process, anodic electrocoating (AEC), cathodicelectrocoating (CEC) has become increasingly established since themid-1970s. It has various advantages: in addition to improved corrosionprotection, mention should be made of homogeneous layer thicknessdistribution, and also better throwing power and good edge coverage.

CEC finds use especially in chassis coating. This process firstlyachieves corrosion protection, and secondly protects the coating fromstonechipping. CEC can be used as a corrosion protection coating for allmetallic substrates; mention should be made here, for example, ofsupports or racks for outside use. Owing to the substantial absence oforganic solvent, environmental compatibility completes the advantages ofcathodic electrocoating as a highly efficient and attractive coatingmethod.

Electrocoat materials in use to date have especially been waterbornecoating materials which usually comprise self-crosslinking orextraneously crosslinking synthetic resins as binders, which can bedispersed through protonation with acid in water. Protonation of thefunctional groups present in the synthetic resins forms ammonium,phosphonium or sulfonium groups. The synthetic resins are, for example,polymerization, polyaddition or polycondensation products containingprimary or tertiary amino groups, such as amino epoxy resins, aminopoly(meth)acrylate resins or amino polyurethane resins. The electrocoatmaterials may contain conventional color pigments, which are generallyorganic and inorganic color pigments. However, the range of color shadeswhich is actually used commercially is very limited. The use of effectpigments in electrocoat material is commercially unknown to date.

The CEC bath contains binder, pigment paste, water-miscible organicsolvent and water. The essential constituent of binder and pigment pasteis frequently epoxy resin. Binder and pigment paste make up the majorityof the about 20% solids content of the coating material. The electrocoatmaterial further consists to an extent of about 80% by weight of water.There is additionally a small portion of organic solvents (1-2%), acids(0.4%) and additives. The epoxy resin is converted to awater-dispersible form by adding a neutralizing agent. An organic acidis used for this purpose (principally acetic acid). Often only a portionof the functional groups is reacted with neutralizing agent. The molarratio of acid to functional group is referred to as the degree ofneutralization. A degree of neutralization of about 30% is sufficient toachieve the desired water dispersibility. An organic acid is also usedto establish the slightly acidic pH in the CEC bath.

DE 10 2005 020 763.4, which was yet to be published at the priority dateof the present application, describes metal effect pigments which canfind use in anodic electrocoat materials.

EP 0 477 433 A1 discloses metal effect pigments coated with syntheticresins, a very thin siloxane layer being applied as an adhesion promoterbetween metal effect pigment surface and the synthetic resin layer. Thisdocument does not make any reference to electrocoating.

EP 0 393 579 B1 discloses a metal pigment-containing waterborne coatingmaterial which is said to be applicable to a substrate by means ofelectrocoating. EP 0 393 579 B1 does not disclose any metal effectpigments suitable for cathodic electrocoating.

It is an object of the present invention to provide metal effectpigments which can be deposited in a coating material on a workpiece incathodic electrocoating.

The metal effect pigments must be corrosion-stable to the aqueouselectrocoat material medium and be depositable reproducibly even aftermore than 60 days of bath time. Electrocoatings thus produced shouldhave a metallic effect whose optical quality preferably corresponds toat least that of powder coatings.

It is a further object of the present invention to find a process forproducing such metal effect pigments.

The object is achieved by providing electrocoat material pigments whichare metal effect pigment platelets coated with at least one coatingmaterial, said coating material comprising

-   (a) one or more functional groups for adhesion or attachment to the    pigment surface and-   (b) at least one amino-functional group, said amino-functional group    being protonatable or positively charged.

Preferred developments of the electrocoat material pigments arespecified in subclaims 2 to 12.

The object is additionally achieved by providing a process for producingelectrocoat material pigments as claimed in one of claims 1 to 12,wherein the process comprises the following steps:

-   (a) coating a metal effect pigment with the coating material having    an amino-functional group dissolved or dispersed in a solvent, said    amino-functional group being protonatable or positively charged,-   (b) optionally drying the metal effect pigments coated with the    coating material in step (a),-   (c) optionally converting the metal effect pigments dried in    step (b) to a paste.

A development of the process according to the invention is specified insubclaim 14.

The object underlying the invention is also achieved by the use ofelectrocoat material pigments as claimed in one of claims 1 to 12 in acathodic electrocoat material or in cathodic electrocoating.

The invention further relates to a cathodic electrocoat materialcomprising electrocoat material pigments as claimed in one of claims 1to 12.

The metal effect pigments may consist of metals or alloys which areselected from the group consisting of aluminum, copper, zinc, tin,brass, iron, titanium, chromium, nickel, steel, silver and alloys andmixtures thereof. Preference is given here to aluminum pigments andbrass pigments, particular preference being given to aluminum pigments.

The metal effect pigments are always platelet-shaped in nature. This isunderstood to mean pigments in which the longitudinal dimension is atleast ten times, preferably at least twenty times and more preferably atleast fifty times the mean thickness. In the context of the invention,when metal effect pigments are mentioned, what is meant is always metaleffect pigment platelets.

The metal effect pigments used in the inventive electrocoat materialpossess mean longitudinal dimensions which are determined as sphereequivalents by means of laser granulometry (Cilas 1064, from Cilas) andare reported as the d₅₀ value of the corresponding cumulative undersizedistribution. These d₅₀ values are 2 to 100 μm, preferably 4 to 35 μmand more preferably 5 to 25 μm.

It has been found that, surprisingly, it is virtually no longer possibleto deposit very large pigment particles with a d₅₀ above 100 μm. Itappears that the migration and deposition properties are considerablyreduced for relatively large particles. From such coarse pigmentdistributions, only the fractions below approx. 100 μm are now deposited(fines fraction). However, this considerably reduces the size and sizedistribution of the particles deposited compared to those used. For thisreason, smaller particles with a d₅₀ of less than <100 μm are preferred.From a d₅₀ of approx. 2 to 35 μm, the inventive pigments are depositedover their entire size distribution without any problems. In addition,pigments from this size enable a bath time of more than 60 days.

Below a d₅₀ of 4 μm, the particles are too fine to produce an appealingvisual effect. Here too, owing to the very high specific surface area ofthe fine pigments, gassing problems can occasionally occur in theaqueous electrocoat medium.

The mean thickness of the inventive metal effect pigments, in contrast,is preferably 40 to 5000 nm, more preferably 65 to 800 nm and mostpreferably 250 to 500 nm.

Electrocoat materials are always waterborne systems. For this reason,metal effect pigments present in an electrocoat material have to bestabilized for use in aqueous systems. For example, they are providedwith a protective layer in order to prevent the corrosive influence ofwater on the metal effect pigment. In addition, they must have suitablesurface charges in order to possess sufficient electrophoretic mobilityin the electrical field.

These properties are surprisingly provided when metal effect pigmentsare coated with a coating material, said coating material having one ormore functional groups for adhesion or attachment to the pigment surfaceand at least one protonatable or positively charged amino-functionalgroup.

In the context of the invention, the term “adhesion” is understood tomean noncovalent interactions, for example hydrophobic interactions,hydrogen bonds, ionic interactions, van der Waals forces, etc., whichlead to immobilization of the coating material on the pigment surface.

In the context of the invention, the term “attachment” is understood tomean covalent bonds which lead to covalent immobilization of the coatingmaterial on the pigment surface.

It has been found, entirely surprisingly, that metal effect pigments incathodic electrocoating have outstanding electrophoretic mobility whenthe metal effect pigments are provided with a coating material whichcontains an amino-functional group.

The protonatable or positively charged amino-functional group, afterintroduction of the coated metal effect pigments into the electrocoatmedium, preferably projects into the electrocoat medium. Theprotonatable or positively charged amino-functional group is preferablyarranged spaced apart from the metal effect pigment surface by a spacer.The spacer is a preferably organic structural element which isunreactive under electrocoating conditions and binds the adhering orattaching group on the metal effect pigment surface and the protonatableor positively charged amino-functional group to one another.

The unreactive organic structural element may, for example, be a linearor branched alkyl chain having 1 to 20 carbon atoms, preferably having 2to 10 carbon atoms, more preferably having 3 to 5 carbon atoms.Optionally, this linear or branched alkyl chain may contain heteroatomsor heteroatom groups such as O, S or NH.

More preferably, the protonatable or positively charged amino-functionalgroup is a terminal, substituted or unsubstituted amino group, i.e. anamino group arranged terminally on the spacer, which is spaced apart tothe maximum degree from the group which provides attachment or adhesionto the metal effect pigment surface.

The amino-functional group is preferably a protonatable amino group or apositively charged amino group.

In one variant of the invention, the positively charged amino-functionalgroup is preferably a quaternary ammonium compound. Such quaternaryammonium compounds are preferably obtained by alkylating aminecompounds.

In a further preferred compound, the charge state can be controlled bylowering the pH, by adding acid to protonate the amino-functionalgroup(s).

In one variant of the present invention, the amino-functional group isan —NH₂ group arranged on the spacer.

In a further variant, the amino-functional group is an —NR¹R² grouparranged on the spacer,

where R¹ and R² may be the same or different from one another and mayeach independently be hydrogen, alkyl having 1 to 20 carbon atoms,preferably having 2 to 10 carbon atoms, more preferably having 3 to 5carbon atoms, orR¹ and R² may be joined to one another and, together with the nitrogenatom, form a heterocycle which preferably contains 4 or 5 carbon atoms.

In a further variant, the amino-functional group is an —NR¹R²R³ grouparranged on the spacer,

where R¹, R² and R³ may be the same or different from one another andmay each independently be hydrogen, alkyl having 1 to 20 carbon atoms,preferably having 2 to 10 carbon atoms, more preferably having 3 to 5carbon atoms.

In a preferred development of the invention, the metal effect pigmentsare provided with an inorganic and/or organic coating, optionally in theform of an inorganic/organic mixed layer, coated with synthetic resin orsurface oxidized so as to inhibit corrosion (ALOXAL® product series fromEckart GmbH & Co.) or colored metal effect pigments (for exampleALUCOLOR® product series from Eckart GmbH & Co.) and treated with atleast one coating material which contains binder functionalitiessuitable for electrocoat materials.

The metal effect pigments coated with synthetic resins contain a coatingof polymers. These polymers are polymerized onto the metal effectpigments proceeding from monomers. The synthetic resins includepolyacrylates, polymethacrylates, polyesters and/or polyurethanes.

In a preferred embodiment, the coated metal effect pigment is coatedwith at least one polymethacrylate and/or polyacrylate.

Particular preference is given to using metal effect pigments which havebeen produced according to the teaching of EP 0 477 433 A1, which ishereby incorporated by reference. Such pigments preferably contain,between the metal effect pigment and the synthetic resin coating, anorganofunctional silane which serves as an adhesion promoter. Particularpreference is given here to coatings composed of preferably multiplycrosslinked polyacrylates and/or polymethacrylates. Such coatingsalready constitute a certain though not completely reliablecorrosion-inhibiting protection against the aqueous medium ofelectrocoat materials. Similar pigments are described in DE 36 30 356C2, an ethylenically unsaturated carboxylic acid and/or phosphoric mono-or diester as an adhesion promoter being arranged here between the metaleffect pigment and the synthetic resin coating.

Examples of such crosslinkers which can be used with preference in thepresent invention are: tetraethylene glycol diacrylate (TEGDA),triethylene glycol diacrylate (TIEGDA), polyethylene glycol-400diacrylate (PEG400DA), 2,2′-bis(4-acryloyloxyethoxyphenyl)propane,ethylene glycol dimethacrylate (EGDMA), diethylene glycol dimethacrylate(DEGDMA), triethylene glycol dimethacrylate (TRGDMA), tetraethyleneglycol dimethacrylate (TEGDMA), butyldiglycol methacrylate (BDGMA),trimethylolpropane trimethacrylate (TMPTMA), 1,3-butanedioldimethacrylate (1,3-BDDMA), 1,4-butanediol dimethacrylate (1,4-BDDMA),1,6-hexanediol dimethacrylate (1,6-HDMA), 1,6-hexanediol diacrylate(1,6-HDDA), 1,12-dodecanediol dimethacrylate (1,12-DDDMA), neopentylglycol dimethacrylate (NPGDMA). Particular preference is given totrimethylolpropane trimethacrylate (TMPTMA).

These compounds are commercially available from Elf Atochem DeutschlandGmbH, D-40474 Dusseldorf, Germany, or Rohm & Haas, In der Kron 4,D-60489 Frankfurt/Main, Germany.

The thickness of the corrosion-inhibiting coating, preferably organiccoating or synthetic resin coating, is preferably 2 to 50 nm, morepreferably 4 to 30 nm and especially preferably 5 to 20 nm. Theproportion of organic coating or synthetic resin coating, based in eachcase on the weight of the uncoated metal effect pigment, depends in theindividual case on the size of the metal effect pigments and ispreferably 1 to 25% by weight, more preferably 2 to 15% by weight andespecially preferably 2.5 to 10% by weight.

The coating material is applied to the metal effect pigments after theapplication of the organic coating or of the synthetic resin layerand/or of another corrosion-inhibiting layer, for example of aninorganic coating such as a metal oxide-containing layer or metal oxidelayer.

The corrosion-inhibiting coating may, for example, comprise essentiallymetal oxide, especially silicon dioxide, or consist thereof. A metaloxide layer can be applied using different processes known to thoseskilled in the art. For example, a silicon dioxide layer can be appliedby means of sol-gel methods with hydrolysis of tetraalkoxysilanes, wherethe alkoxy group may be methoxy, ethoxy, propoxy or butoxy. However, itis also possible to apply an SiO₂ coating to the metal effect pigmentsurface using waterglass.

The corrosion-inhibiting coating may also be a surface oxide layer. Forexample, it is possible to provide aluminum effect pigments with animpervious surface oxide layer which is corrosion-inhibiting withrespect to aqueous media.

In a preferred embodiment, the oxide layer may additionally comprisecolor pigments. The color pigments can be introduced during theapplication of the metal oxide layer, especially silicon dioxide layer,or during the surface oxidation of the surface of the metal oxide layer.

The corrosion-inhibiting coating, for example synthetic resin layer, maycompletely surround the pigments, but it may also be present in notentirely continuous form or have cracks. Use of the coating materialwith protonatable or positively charged amino-functional group and withfunctional groups for adhesion and/or attachment to the pigment surfacein the present invention covers possible corrosion sites which can becaused by such cracks or by an incomplete corrosion-inhibiting coatingon the metal effect pigment.

The coating material used in the present invention is capable,especially when it attaches to the metallic pigment surface, ofpenetrating into such gaps or cracks in the corrosion-inhibitingcoating, preferably synthetic resin coating, thus bringing about therequired corrosion stability.

Even though it has been found that, surprisingly, the coating materialused in the present invention also has corrosion-inhibiting propertiesin the case of metal effect pigments, this coating material is usedprimarily in order to make the metal effect pigments cathodicallydepositable. The coating material with protonatable or positivelycharged amino-functional group makes the metal effect pigmentselectrophoretically mobile in the electrocoating bath, i.e. they migratein the direction of the object to be coated which is connected as thecathode.

Metal effect pigments which are coated only with synthetic resin orother corrosion-inhibiting coatings and have not been treated with thecoating material with amino-functional group used in the presentinvention can be cathodically deposited only insufficiently, or cannotbe cathodically deposited effectively, in cathodic electrocoating.

In electrocoating, conventional color pigments added to an electrocoatmaterial are deposited on the workpiece by a comparatively randomprocess. The electrocoat material is always stirred vigorously hereduring the deposition. As a result, essentially mass transfer toward theworkpiece takes place (convection). Only within the Nernst diffusionlayer which forms does electrophoretic migration of the charged binderparticles within the electrical field proceed. The concentration of thecolor pigments in the deposition bath is very high (approx. 10% byweight). The binder which is deposited entrains the color pigments.There is no electrophoretic migration of the color pigments in theelectrical field.

Metal effect pigments are not usable per se in electrocoat materials.Even if they are corrosion-stable to the aqueous medium of theelectrocoat material as a result of a suitable protective layer, forexample a metal oxide or a synthetic resin, they are either not or areno longer deposited after a few hours to days after an initialdeposition, which is referred to as inadequate bath stability.

It has been found that, surprisingly, the inventive metal effectpigments can be deposited reliably and over long periods in cathodicelectrocoating, and the electrocoat material has a bath stability ofmore than 60 days. The inventive metal effect pigments present in thecathodic electrocoat material are therefore deposited reliably on theworkpiece even after 60 days, preferably after 90 days. Moreover, theyhave sufficient corrosion stability, such that no significant gassing(in the case of aluminum or iron pigments) or release of metal ions (inthe case of brass pigments) occurs within this time in the electrocoatmaterial.

It has been found that the coating material in this case must have oneor more amino-functional groups. These are at least partly protonated inthe electrocoat material. These protonated amino groups are thought toimpart sufficient positive surface charges to the inventive electrocoatmaterial pigment to be well-dispersed in the predominantly aqueousmedium of the electrocoat material. Moreover, the inventive metal effectpigments are thought to be positively charged at their surface such thatmigration in the electrical field applied toward the cathode is enabledwithin the Nernst diffusion layer. It is thought that the surface of theinventive metal effect pigments is matched chemically in this way to thebinders of the cathodic electrocoat material. This enables the effectthat the metal effect pigments can firstly migrate electrophoreticallyin the electrical field and secondly take part in the depositionmechanism of the electrocoat materials at the cathode.

Furthermore, the coating materials contain functional groups which bringabout or can bring about adhesion and/or attachment to the surface ofthe metal effect pigment or the stabilizing coating thereof. The pigmentsurface may directly be the metal effect pigment surface. The pigmentsurface may, however, also be the metal effect pigment surface coatedwith an inorganic or organic coating, preferably with synthetic resin.In this way, the coating materials can be anchored to the metal effectpigments reliably and to a sufficient degree.

These functional groups for adhesion or attachment to the coated oruncoated metal effect pigment surface are, for example, phosphonicester, phosphoric ester, carboxylate, metallic ester, alkoxysilyl,silanol, sulfonate, hydroxyl, polyol groups, and mixtures thereof.Particular preference is given to the alkoxysilyl and/or silanol groupsof suitable organofunctional silanes.

Such functionalized coating materials contribute to the corrosionstability of the metal effect pigments in the aqueous electrocoatmaterial. For example, in the case of iron or aluminum pigments,gassing, i.e. evolution of hydrogen, can surprisingly be suppressedeffectively.

It has been found to be essential that the coating material mustnecessarily have at least one protonatable or positively chargedamino-functional group and at least one functional group for adhesion orattachment to the pigment surface. For example, aliphatic amines whichlack the at least one functional group for adhesion or attachment to thepigment surface are unsuitable for providing metal effect pigments whichare effectively cathodically depositable in a cathodic electrocoatmaterial system.

In the inventive electrocoat material pigments, preference is given tousing, as coating materials, amines which can be protonated to ammoniumsalts. Particularly preferred coating materials compriseamino-functional silanes of the formula

R¹ _(a)R² _(b)Si(OR′)_((4-a-b))  (I)

where R¹ is an organofunctional group which contains at least oneamino-functional group, R² is a further organofunctional group whichdoes not contain an amino-functional group, R′ is independently H or analkyl group having 1 to 6 carbon atoms, preferably having 1 to 3 carbonatoms, and wherea and b are integers, with the proviso that a may be 1 to 3 and b may be0 to 3, where a and b in total are not more than 3.R′ is preferably ethyl or methyl.R² is preferably substituted or unsubstituted alkyl having preferably 1to 6 carbon atoms, for example methyl or ethyl. In addition, R² may besubstituted by functional groups, for example acrylate, methacrylate,vinyl, isocyanato, hydroxyl, carboxyl, thiol, cyano, epoxy or ureidogroups.

In a preferred embodiment, b=0. In a particularly preferred embodiment,a=1 and b=0.

The at least one protonatable or positively charged amino-functionalgroup which contains R¹ is preferably a primary, secondary, tertiaryamine or an ammonium group. The amino-functional group is preferably asdefined above.

Such silanes are commercially available. For example, these are manyrepresentatives of the products which are produced by Degussa,Rheinfelden, Germany and are sold under the trade name Dynasylan®, orthe Silquest® silanes produced by OSi Specialties, or the GENOSIL®silanes produced by Wacker, Burghausen, Germany.

Examples thereof are N-benzyl-N-aminoethyl-3-aminopropyltrimethoxysilane(Dynasylan 1161),N-vinylbenzyl-N-(2-aminoethyl)-3-aminopropylpolysiloxane (Dynasylan1172), N-vinylbenzyl-N-(aminoethyl)-3-aminopropylpolysiloxane (Dynasylan1175), aminopropyltrimethoxysilane (Dynasylan AMMO; Silquest A-1110),aminopropyltriethoxysilane (Dynasylan AMEO) orN-(2-aminoethyl)-3-aminopropyltrimethoxysilane (Dynasylan DAMO, SilquestA-1120) or N-(2-aminoethyl)-3-aminopropyltriethoxysilane,triamino-functional trimethoxysilane (Silquest A-1130),bis-(gamma-trimethoxysilylpropyl)amine (Silquest A-1170),N-ethyl-gamma-aminoisobutyltrimethoxysilane (Silquest A-link 15),N-phenyl-gamma-aminopropyltrimethoxysilane (Silquest Y-9669),4-amino-3,3-dimethylbutyltrimethoxy-silane (Silquest Y-11637),N-cyclohexylaminomethyl-methyldiethoxysilane (GENIOSIL XL 924),(N-cyclohexylaminomethyl) triethoxysilane (GENIOSIL XL 926),(N-phenylaminomethyl)trimethoxysilane (GENIOSIL XL 973),aminopropyldimethylethoxysilane, aminopropylmethyldiethoxysilane,N-methylaminopropyl-dimethylethoxysilane,N-methylaminopropylmethyl-diethoxysilane,N-methylaminopropyltriethoxysilane,N-ethylaminopropyldimethylethoxysilane,N-ethylamino-propylmethyldiethoxysilane,N-ethylaminopropyl-triethoxysilane,N-cyclohexylaminopropyltriethoxy-silane,N-cyclohexylaminopropylmethyldiethoxysilane,N-phenylaminotriethoxysilane, N-phenylaminopropyl-triethoxysilane,N,N-dimethylaminopropyldimethylethoxy-silane,N,N-dimethylaminopropylmethyldiethoxysilane,N,N-dimethylaminopropyltriethoxysilane,N,N-diethyl-aminopropyldimethylethoxysilane,N,N-diethylamino-propylmethyldiethoxysilane,N,N-diethylaminopropyl-triethoxysilane,N,N-dipropylaminopropyldimethyl-ethoxysilane,N,N-dipropylaminopropylmethyl-triethoxysilane,N,N-dipropylaminopropyltriethoxy-silane,N,N-methylethylaminopropyldimethylethoxysilane,N,N-methylethylaminopropylmethyldiethoxysilane,N,N-methylethylaminopropyltriethoxysilane,anilinopropyldimethylethoxysilane, anilinopropylmethyldiethoxysilane,anilinopropyltriethoxysilane, morpholinopropyldimethyl-ethoxysilane,morpholinopropylmethyldiethoxysilane, morpholinopropyltriethoxysilane,N,N,N-trimethyl-ammoniumpropyldimethylethoxysilane,N,N,N-trimethylammoniumpropylmethyldiethoxysilane,N,N,N-trimethylammoniumpropyltriethoxysilane,N,N,N-triethyl-ammoniumpropyldimethylethoxysilane,N,N,N-triethylammoniumpropylmethyldiethoxysilane,N,N,N-triethylammoniumpropyltriethoxysilane,trimethoxysilylpropyl-substituted polyethyleneimine,dimethoxymethylsilylpropyl-substituted polyethyleneimine and mixturesthereof.

The coating materials with protonatable or positively chargedamino-functional group are preferably used in amounts of 1 to 100% byweight based on the weight of the uncoated metal effect pigment. Below1% by weight, the effect may be too minor, such that the metal effectpigments can no longer be deposited reliably, especially after more than60 days of bath time. Above 100% by weight, an unnecessarily largeamount of coating material with amino-functional group is used. Inaddition, excess coating material with an amino-functional group canadversely affect the properties of the electrocoat material. The coatingmaterial(s) with an amino-functional group are preferably used inamounts of 5 to 70% by weight and especially preferably of 7 to 50% byweight, more preferably of 10 to 30% by weight, based in each case onthe weight of the metal effect pigment uncoated with coating material.These figures are based in each case on the coating material itself andnot on any solvent which is possibly present and in which the coatingmaterial with an amino-functional group is supplied in its commerciallyavailable administration form.

The coating material may, but need not, completely surround the metaleffect pigments.

A process for providing the inventive metal effect pigments comprisesthe coverage of the metal effect pigment with the coating material withan amino-functional group. It comprises the following steps:

-   (a) coating a metal effect pigment with the coating material having    an amino-functional group dissolved or dispersed in a solvent, said    amino-functional group being protonatable or positively charged,-   (b) optionally drying the metal effect pigments coated with the    coating material in step (a),-   (c) optionally converting the metal effect pigments dried in    step (b) to a paste.

The coverage can take place in many different ways. The metal effectpigment can be initially charged, for example, in a mixer or kneader inthe form of a paste, for example in an organic solvent or in a mixtureof organic solvent and water. Subsequently, the coating material with aprotonatable or positively charged amino-functional group is added andallowed to act on the metal effect pigment preferably for at least 5min. The coating material is preferably added in the form of a solutionor dispersion. This may be an aqueous solution or a predominantlyorganic solution.

In addition, the metal effect pigment can first be dispersed in asolvent. The coating material is then added thereto with stirring. Inthis case, the solvent in which the coating material is dissolved shouldpreferably be miscible with that in which the metal effect pigment isdispersed. If required, higher temperatures up to the boiling point ofthe solvent or of the solvent mixture can be established, but roomtemperature is usually sufficient to apply the coating materialeffectively to the metal effect pigment.

Thereafter, the pigment is freed from the solvent and either dried togive the powder and/or optionally converted to a paste in anothersolvent. Useful solvents include water, alcohols, for example ethanol,isopropanol, n-butanol, or glycols, for example butylglycol. The solventshould be miscible with water. The inventive pigment is traded as apaste or powder. The pastes have a nonvolatile component of 30 to 70% byweight based on the weight of the overall paste. The paste preferablyhas a nonvolatile component of 40 to 60% by weight and more preferablyof 45 to 55% by weight.

The paste form is a preferably dust-free and homogeneous preparationform of the inventive electrocoat material pigments. The inventiveelectrocoat material pigments may also be present in dust-free andhomogeneous form as pellets, sausages, tablets, briquettes or granules.The aforementioned preparation forms can be produced in the manner knownto those skilled in the art by pelletization, extrusion, tabletting,briquetting or granulation. In these compacted preparation forms, thesolvent has substantially been removed. The residual solvent content istypically within a range of less than 15% by weight, preferably lessthan 10% by weight, more preferably between 0.5 and 5% by weight, basedin each case on the weight of the pigment preparation.

The coating material with a protonatable or positively chargedamino-functional group may, before the coating of the metal effectpigment, be present in a neutralized or partly neutralized form.However, it can also be neutralized after the coating operation. Theneutralization/partial neutralization can also not be effected until thepH adjustment of the electrocoat material.

Customary acids are suitable for neutralization of the basicfunctionalities. Examples thereof are: formic acid, acetic acid,hydrochloric acid, sulfuric acid or nitric acid, or mixtures of theseacids. A sufficient amount of acid should be used that at least 25%,preferably 40%, of the basic groups of the metal effect pigment coveredwith the coating material are present in neutral form. In this context,basic groups also include functional groups which may originate from themetal effect pigment itself.

It is also possible to combine steps (a) and (b) of the processaccording to the invention to one step, by applying the coating materialas a solution or dispersion to metal effect pigments moving in a gasstream.

In a particular embodiment, the inventive electrocoat material pigmentscan be produced by a process with the following steps:

-   a) producing a solution or dispersion of the coating material with    protonatable or positively charged amino-functional group in an    organic solvent,-   b) coating the metal effect pigment with the coating material by    -   i) dispersing the metal effect pigment in the solution or        dispersion of a) and then spraying or    -   ii) spraying the solution or dispersion from a) onto metal        effect pigments fluidized in a gas stream,-   c) optionally drying the metal effect pigments coated with binder in    a moving gas stream,-   d) optionally converting the pigment to paste in water and/or an    organic solvent,-   e) optionally neutralizing with an acid.

The pigments can be neutralized and converted to paste as describedabove.

Preference is given to combining steps b) and c) in one process step, byperforming the spraying and drying in a spray drier.

Preference is given to using volatile solvents, for example acetoneand/or ethyl acetate.

The inventive electrocoat material pigments are used in cathodicelectrocoat materials or in cathodic electrocoating.

The invention further provides a cathodic electrocoat materialcomprising the inventive electrocoat material pigments, a binder andwater. The binders are, for example, polymerization, polyaddition orpolycondensation products containing primary or tertiary amino groups,for example amino epoxy resins, amino poly(meth)acrylate resins or aminopolyurethane resins. In addition, further customary additions such asfillers, additives, organic and/or inorganic color pigments, etc. may bepresent in the electrocoat material.

By means of acids, the amino groups of the binders and preferably theamino groups of the coating material of the inventive electrocoatmaterial pigments are at least partly protonated. This has the effectthat the binders and the inventive electrocoat material pigments movetoward the cathode in the applied electrical field and take part in thedeposition mechanism of the cathodic electrocoating. The coatingsobtained in this way have an attractive metal effect which has beenunknown to date in cathodic electrocoat material and are exceptionallyabrasion-stable.

The inventive electrocoat material pigments can optionally also beneutralized as early as after the coating with coating material.

The examples which follow illustrate the invention in detail, butwithout restricting it.

INVENTIVE EXAMPLE 1

46.5 g of PCA 9155 (aluminum pigment coated with organic polymers, withD₅₀=18 μm; from Eckart GmbH & Co. KG, Fürth, Germany) are mixed with asolution of 7 g of Dynasylan 1161(N-benzyl-N-aminoethyl-3-aminopropyltrimethoxysilane from Degussa,Germany) in 46.5 g of butylglycol to give a homogeneous pigment paste.

INVENTIVE EXAMPLE 2

46.5 g of PCA 9155 (aluminum pigment coated with organic polymers, withD₅₀=18 μm; from Eckart GmbH & Co. KG, Fürth, Germany) are mixed with asolution of 7 g of Dynasylan 1172(N-vinylbenzyl-N-(2-aminoethyl)-3-aminopropylpolysiloxane from Degussa,Germany) in 46.5 g of butylglycol to give a homogeneous pigment paste.

The paste is dried cautiously in a vacuum drying cabinet at approx. 60°C. to give the powder.

INVENTIVE EXAMPLE 3

46.5 g of PCA 9155 (aluminum pigment coated with organic polymers, withD₅₀=18 μm; from Eckart GmbH & Co. KG, Fürth, Germany) are mixed with asolution of 7 g of Dynasylan 1175(N-vinylbenzyl-N-(aminoethyl)-3-aminopropylpolysiloxane from Degussa,Germany) in 46.5 g of butylglycol to give a homogeneous pigment paste.

INVENTIVE EXAMPLE 4

The preparation is effected as in Example 3, but with an aluminum effectpigment of greater particle size D₅₀=32 μm, PCA 214 (from Eckart GmbH &Co. KG).

Production of the Electrocoat Materials and Testing Thereof:

27 g of the pastes from Examples 1, 3 or 4 are admixed with 27 g ofbutylglycol.

15 g of the powder from Example 2 are admixed with 39 g of butylglycol.

10 g of VEK 40871-02 CEC binder (800 by weight epoxy resin from Cytech,Austria) and 1.5 g of wetting agent (from FreiLacke, Bräunlingen,Germany), 465 g of VEK 40871-0-03 CEC binder (34.5% by weight epoxyresin from Cytech, Austria) and 662 g of water are added.

The dip-coating materials produced according to this formulation forcathodic dip-coating feature a viscosity of 9±1 seconds, measured at atemperature of 20° C. in a DIN 4 flowcup. The electrocoat materialspossess a solids content of 13 to 17% by weight based on the weight ofthe overall electrocoat material. The proportion of the aluminumpigments is approx. 1% by weight. The measured pH of the electrocoatingbaths at 25° C. is a pH of about 5.5 to 6.5.

COMPARATIVE EXAMPLE 1

PCA 9155 (from Eckart GmbH & Co. KG), a synthetic resin-coated aluminumeffect pigment of mean particle size D₅₀=18 μm in paste form (solids 50%by weight) is used in the electrocoat material without further coating.In contrast to inventive example 1, 7 g of Dynasylan 1161 coatingmaterial are introduced here into the electrocoating bath only onaddition of the commercial cathodic dip-coating material (from FreiLacke).

COMPARATIVE EXAMPLE 2

PCA 9155 (from Eckart GmbH & Co. KG), a synthetic resin-coated aluminumeffect pigment of mean particle size D₅₀=18 μm in paste form (solids 50%by weight) without further coating.

Here, no further additive (coating material) is added to the dip-coatingmaterial.

The electrochemical deposition operation is effected in an electricallyconductive vessel, a so-called tank, which consists of an electricallyconductive material and is connected as the anode in the circuit. Theworkpiece to be coated, in the inventive example a metal sheet ofdimensions 7.5 cm×15.5 cm is connected as the cathode and immersed intothe electrocoating bath for ⅔ of its length.

In order to prevent sedimentation and the formation of dead spaces, theelectrocoat material is moved with a mean flow rate of approx. 0.1 m/s.Subsequently, a voltage of 100 V is applied over a period of 120seconds. The temperature of the electrocoating bath is 30° C. Theworkpiece thus coated is subsequently rinsed off thoroughly withdistilled water in order to remove residues of uncoagulated resin. Theworkpiece is then left to vent for a period of 10 minutes. Subsequently,the electrocoat material is crosslinked and fired at 170° C. for 20minutes. The coating layer thickness thus achieved is 30±2 μm.

The cathodic electrocoat materials produced with the pigments frominventive examples 1 to 4 have an exceptionally high storage anddeposition stability in relation to the aluminum effect pigments presenttherein. This is evident from Table 1. The coating materials were storedat room temperature and, within a time interval of 7 days, metal sheetsas described above were electrocoated. These tests were stopped after 60days.

In addition, samples of inventive examples 1 to 4 were stored at 40° C.for 30 days. Subsequently, they were incorporated into an electrocoatingmaterial as described above, and metal sheets were electrocoated. Withregard to the optical properties of these applications, no differencefrom applications with freshly produced samples were found.

Gassing tests were carried out with the electrocoat materials producedusing the pigments from inventive examples 1 to 4 and comparativeexamples 1 and 2. For this purpose, 250 g of the electrocoat materialswere heat treated at 40° C. in a gas bottle with a double chamber tubeattachment, and the amount of gas evolved (H₂, which is formed by thereaction of the aluminum effect pigments with water) is measured. Thetest is considered to be passed when not more than 20 ml of hydrogenhave evolved after 30 days.

The test results are compiled in Table 1.

TABLE 1 Performance of the cathodic dip-coating materials which havebeen produced using the pigments from examples 1 to 4 and comparativeexamples 1 and 2. Deposition Gassing after stability 30 days Sample (ind) (ml of H₂) Example 1 >60 d 12 Example 2 >60 d 5 Example 3 >60 d 10Example 4 >60 d 6 Comparative example 1  <7 d 12 Comparative example 2 <7 d After 10 days >25 ml

For the electrocoat materials comprising pigments of inventive examples1 to 4, reproducible results with regard to the visual appearance of thecoated test sheets were obtained even after more than 60 days of storagetime at room temperature. Moreover, they did not exhibit any significantgassing in the aqueous electrocoat materials.

The electrocoat material comprising pigments of comparative example 1was likewise gassing-stable, but had virtually no deposition stability.The aluminum effect pigments not provided with a coating of comparativeexample 2 are neither gassing-stable in the electrocoat material nor dothey possess sufficient deposition stability.

COMPARATIVE EXAMPLE 3 Metal Effect Pigment-Containing Powder CoatingMaterial

9 g of a commercial metal effect pigment for powder coating material,Spezial PCA 214, d50=32 μm (from Eckart GmbH & Co. KG), are mixedintimately in a plastic bag with 291 g of a powder clearcoat material,AL 96 Polyester PT 910 System (from DuPont) and 0.6 g of a “free-flowadditive”, Acematt OK 412 (from Degussa). The contents are subsequentlytransferred directly into a mixing vessel which approximates to acommercial kitchen mixer in terms of construction and form (Thermomixfrom Vorwerk), and mixed at a moderate stirrer speed level at 25° C. for4 minutes. This procedure corresponds to the “dry-blend method” commonin powder coating materials. The powder coating material thus producedis applied by means of the customary corona discharge technique (GEMAelectrostatic spray gun PG 1-B) to a customary test sheet (“Q panel”).The application conditions of the powder coating technique applied herecorresponds to the following: powder hose connection: 2 bar; purge airconnection: 1.3 bar; voltage: 60 kV; material flow regulator: approx.500; gun-sheet distance: approx. 30 cm.

This is followed by the firing and the crosslinking of the powdercoating material system in an oven. The firing time is 10 minutes at atemperature of 200° C. The dry layer thickness to be achieved in thisprocess is 50-75 μm.

COMPARATIVE EXAMPLE 4 Metal Effect Pigment-Containing Powder CoatingMaterial

As comparative example 3, except that the metal effect pigment used wasSpezial PCA 9155, d50=16 μm (from Eckart GmbH & Co. KG).

The different applications in inventive examples 1 to 4 were comparedwith the substrates of comparative examples 3 and 4 coated by powdercoating technology. For comparative assessment, as is evident frominventive examples 1 to 4 and comparative examples 3 and 4, aluminumeffect pigments of similar particle size and coloristic properties wereused.

Surprisingly, the applications in inventive examples 1 to 4 exhibitexcellent covering capacity, which corresponds in terms of goodness andquality to the powder coating material of comparative examples 3 and 4.

The optical properties are compared via the visual impression of theobserver. It is found here that, surprisingly, inventive examples 1 to 4have no significant differences with regard to brightness and metalliceffect from the conventional powder coating material application incomparative examples 3 and 4.

For the assessment of the optical properties, reference is made to DIN53230. In the testing of paints, coating materials and similar coatings,the properties and/or changes therein often have to be assessedsubjectively. For this case, DIN 53 230 lays down a homogeneousassessment system. This describes how test results which cannot bereported by means of directly obtained measurements should be assessed.

To assess the coating materials which have been obtained with pigmentsaccording to inventive examples 1 to 4 and comparative examples 1 to 4,reference is made to the “fixed rating scale” explained under 2.1 in DIN53 230. This fixed rating scale constitutes a scale for assessing thedegree of properties. In this, the best possible value is designatedwith the index 0, the lowest possible value with the index 5, the term“lowest possible value” being understood to mean that a change ordeterioration over and above this value is no longer of interest inperformance terms. Tab. 2 reproduces the coloristic and opticalproperties determined in relation to DIN 53 230 section 2.1. The indicesare determined by the subjective impression of several test subjects. Inall cases, an agreement of the subjective impression of the assessingtest subjects could be found.

TABLE 2 Visual comparison of the electrocoat material applications ofthe pigments of inventive examples 1 to 4, of comparative examples 1 to2 and of the powder coating material applications of comparativeexamples 3 and 4 Mean particle Covering size D₅₀ capacity BrightnessGeneral visual Sample [μm] [index] [index] impression Inventive 18 0 1Very metallic, example 1 relatively minor “sparkling” effect Inventive18 0 1 Very metallic, example 2 relatively minor “sparkling” effectInventive 18 0 1 Very metallic, example 3 relatively minor “sparkling”effect Inventive 32 1 0 Very good metallic, example 4 “sparkling” effectComparative 18 3 3 Relatively minor example 1 metallic effect as aresult of lack of covering capacity Comparative 18 5 5 Virtually nometal example 2 effect pigment deposited Comparative 32 0 1 Very goodmetallic, example 3 “sparkling” effect Comparative 16 0 0 Very metallic,example 4 relatively minor “sparkling” effect

It can be seen from the comparison displayed above that the applicationswith the inventive electrocoat material pigments and pigmentpreparations according to examples 1 to 4 are comparable with regard tooptical properties with the powder coating material pigments andapplications which have already been established on the market for manyyears. From the comparison of the indices of the electrocoatings whichhave been obtained using inventive examples 1 to 4 with the powdercoatings in comparative examples 3 and 4 shows clearly that the opticalproperties are virtually identical to one another in relation tocoverage, shine and metallic effect.

The coatings in comparative example 1, in which the coating material wasonly introduced directly into the electrocoat material production in thelast step thereof, have deviations. In these variants, significantlosses are found with regard to coverage, shine and, associated withthese, in the metallic effect.

A metal effect pigment treated without coating material (comparativeexample 2) virtually cannot be deposited in the cathodic electrocoatmaterial or in the electrocoating, even though the metal effect pigmenthas a synthetic resin shell.

It is suspected that it is necessary that the coating material withprotonatable or positively charged amino-functional group has to beapplied directly to the metal effect pigment and cannot be added laterto the electrocoat material. It is further suspected that the coatingmaterial with its functional groups for adhesion or attachment forms aphysisorptive and/or chemisorptive adhesion or attachment to the pigmentsurface, which then appears to play a crucial key role in the depositionperformance of the pigment.

1. An electrocoat material pigment, said electrocoat material pigmentcomprising metal effect pigment platelets coated with at least onecoating material, said coating material comprising a) one or morefunctional groups for adhesion or attachment to the pigment surface andb) at least one amino-functional group, said amino-functional groupbeing protonatable or positively charged.
 2. The electrocoat materialpigment as claimed in claim 1, wherein the metal effect pigments have acoating which inhibits corrosion by aqueous systems or media.
 3. Theelectrocoat material pigment as claimed in claim 1, wherein the metaleffect pigments are selected from the group comprising metal effectpigments provided with at least one of inorganic and organic coatings,metal effect pigments provided with inorganic/organic mixed layers,metal effect pigments coated with synthetic resin, surface-oxidizedmetal effect pigments and colored metal effect pigments.
 4. Theelectrocoat material pigment as claimed in claim 1, wherein the metaleffect pigment platelets consist of metals or alloys which are selectedfrom the group consisting of aluminum, copper, zinc, tin, brass, iron,titanium, chromium, nickel, steel, silver and alloys and mixturesthereof.
 5. The electrocoat material pigment as claimed in claim 3,wherein the synthetic resin coating of the metal effect pigmentcomprises at least one of a polyacrylate, a polymethacrylate and acombination thereof.
 6. The electrocoat material pigment as claimed inclaim 2, wherein the corrosion-inhibiting coating consists essentiallyof a metal oxide.
 7. The electrocoat material pigment as claimed inclaim 2, wherein the corrosion-inhibiting coating is a surface oxidelayer.
 8. The electrocoat material pigment as claimed in claim 6 whereinthe oxide layer additionally comprises color pigments.
 9. Theelectrocoat material pigment as claimed claim 1, wherein the coatingmaterial has one or more functional groups for adhesion or attachment tothe metal effect pigment surface or to at least one of a synthetic resinsurface and an inorganic coating applied to the metal effect pigmentsurface.
 10. The electrocoat material pigment as claimed in claim 9,wherein one or more functional groups of the coating material areselected from the group consisting of phosphonic ester, phosphoricester, carboxylate, metallic ester, alkoxysilyl, silanol, sulfonate,hydroxyl, polyol groups and mixtures thereof.
 11. The electrocoatmaterial pigment as claimed in claim 1, wherein the coating material isapplied to the pigment in an amount of 1 to 100% by weight based on theweight of the metallic component of the metal effect pigment.
 12. Theelectrocoat material pigment as claimed in claim 1, wherein the coatingmaterial is a cathodic electrocoat material binder.
 13. A process forproducing electrocoat material pigments as claimed in claim 1, whereinthe process comprises the following steps: (a) coating a metal effectpigment with the coating material having an amino-functional groupdissolved or dispersed in a solvent, said amino-functional group beingprotonatable or positively charged, (b) optionally drying the metaleffect pigments coated with the coating material in step (a), and (c)optionally converting the metal effect pigments dried in step (b) to apaste.
 14. The process as claimed in claim 13, wherein steps (a) and (b)are combined into a single step, by applying the coating material as asolution or dispersion to metal effect pigments moving in a gas stream.15. A method of making a cathodic electrocoat material for use incathodic electrocoating, said method comprising incorporating into saidcathodic electrocoat material a plurality of electrocoat materialpigments as claimed in claim
 1. 16. A cathodic electrocoat materialcomprising electrocoat material pigments as claimed in claim
 1. 17. Theelectrocoat material pigment as claimed in claim 6, wherein the metaloxide is silicon dioxide.